An allergen is an otherwise harmless substance that causes an allergic reaction. Allergic rhinitis, or hay fever, is an allergic response to specific allergens. Pollen is the most common allergen in seasonal allergic rhinitis. These are allergy symptoms that occur with the change of seasons. Between 10 and 30 percent of the worldwide population may also have allergic rhinitis.
When your body comes into contact with an allergen, it releases histamine, which is a natural chemical that defends your body from the allergen. This chemical can cause allergic rhinitis and its symptoms, including a runny nose, sneezing, and itchy eyes.
In addition to tree pollen, other common allergens include:
animal dander, which is old skin
During certain times of the year, pollen can be especially problematic. Tree and flower pollens are more common in the spring. Grasses and weeds produce more pollen in the summer and fall.
The two types of allergic rhinitis are seasonal and perennial. Seasonal allergies usually occur during the spring and fall season and are typically in response to outdoor allergens like pollen. Perennial allergies can occur year round, or at any time during the year in response to indoor substances, like dust mites and pet dander.